Fuel combustion in internal combustion engines typically produce oxides of nitrogen (NOx) and particulate matter, such as soot and ash. Such exhaust by-products, however, are generally undesirable and efforts are continuously being made to further reduce the levels of these exhaust by-products. Developing ways to minimize the levels of these exhaust by-products, however, often involves a balancing between achieving acceptable reduction levels and maintaining combustion efficiency.
Various combustion chamber designs have been attempted to reduce the generation of NOx and particulate matter without sacrificing combustion efficiency. For example, the structural shape of the combustion bowl, which is generally disposed in the combustion face of a piston and defines a portion of the combustion chamber, may be configured to produce a desired distribution of fuel and air in the combustion chamber.
Japanese Patent Application Publication JP2004190573A (the '573 publication) discloses a combustion chamber for an engine with a cavity formed in the top surface of the piston. The cavity includes recesses providing a stepped shape. The stepped shape of the combustion chamber aims to promote the mixing of fuel and air by spreading fuel to recesses of the cavity. While the object of the combustion chamber of the '573 publication is to reduce NOx generation, improvements in reducing particulate matter continue to be sought.